In my experience, those that asked to be referred to as they/them identify as being non-binary, though in reading more on the topic, this is not always the case.

I only adopt the pronouns of those that the person in question expressly asks to be referred to as. Otherwise, if the pronouns are not explicitly mentioned, I default to the pronouns of the gender I perceive said individual to be presenting as until otherwise corrected.

In my opinion, it's simply a sign of mutual respect and acknowledgement that I recognize their identity as they proclaim it to be.